The present disclosure relates to an anode current collector containing an electrolytic copper foil, an anode using the same, and a secondary battery using the same.
In recent years, as portable electronic devices such as a video tape recorder (VTR), a mobile phone, and a mobile computer have been sophisticated and multi-functionalized, a higher capacity of secondary batteries as a power source for these portable electronic devices has been demanded. In the lithium ion secondary battery using graphite for the anode that is generally used currently, the technology thereof has been matured. Thus, the battery capacity thereof is in a saturated state and it is difficult to vastly increase the capacity thereof. Therefore, it is considered to use silicon for the anode. Recently, forming an anode active material layer on an anode current collector by vapor-phase deposition method or the like has been reported. Silicon is largely expanded and shrunk associated with charge and discharge, and thus there has been a problem that the cycle characteristics are lowered due to pulverization. However, if the vapor-phase deposition method is used, such pulverization is able to be inhibited, and the anode current collector and the anode active material layer are able to be integrated. In result, electron conductivity in the anode becomes extremely favorable, and high performance both in the capacity and the cycle life is expected.
However, there has been a problem that even in the anode in which the anode current collector and the anode active material layer are integrated as above, if charge and discharge are repeated, intense expansion and shrinkage of the anode active material layer cause a stress between the anode current collector and the anode active material layer, for example, the anode active material layer is dropped, leading to lowering of the cycle characteristics. Therefore, it has been already considered that the contact characteristics between the anode active material layer and the anode current collector are improved by roughening the surface of the anode current collector (for example, refer to WO 01/031723 pamphlet and Japanese Unexamined Patent Application Publication No. 2002-313319).
However, in the case where the thickness and the volume density of the anode active material layer are increased or the thickness of the anode current collector is decreased in order to further increase the capacity, due to expansion and shrinkage of the anode active material layer, the anode current collector is elongated and distorted. In result, there is a possibility that it leads to deterioration of the cycle characteristics. Further, in the case where the thickness and the volume density of the anode active material layer are increased, the heat value of the anode active material layer in charge and discharge is increased. Thus, from a safety standpoint, it is necessary to inhibit temperature rise of the battery by increasing heat release efficiency of the anode current collector. In the case where the thickness of the anode current collector is decreased, the heat release efficiency is lowered or the electric resistance is increased, resulting in tendency that the heat value of the anode current collector itself is increased. Thus, it is necessary to inhibit temperature rise of the battery by increasing heat release efficiency of the anode current collector as well.
In view of the foregoing disadvantages, it is desirable to provide an anode current collector with a higher mechanical strength and superior heat release characteristics. Further, it is desirable to provide an anode and a secondary battery that include the foregoing anode current collector and have superior cycle characteristics and high safety.